Thanks, I'm hoping to give it more of a polish for the 1.0 release. It's still missing some features that I think are necessary.
To delete a group, select it, and click on the "gear" icon on the bottom left. There's a menu item to "Delete Group".
Did you expect the delete key to delete a group? Or did you right click on a group looking for a menu to delete? I should implement those features, I want the UI to be clear for everyone.
If more people request it, I might make an option in the preferences to have it act like a normal app so you can cmd+tab to it.
I know that you want the app to appear when you need it, but I personally would like it to stay as a normal app after I unhide it and cmd+tab on it.